How do I take care of a potted Hydrangea Macrophylla Glory Blue?

Question:I Just bought a Glory Blue and I've read that you can have pink flowers by making the soil alkaline. How do I do that? What kind of potting soil should I buy? Plant food? Sun or shade? Water amount? Anything you can tell me about the bush would be helpful.

Answers:
Hydrangeas are relatively easy to grow in well-drained soils containing plenty of organic matter. They prefer warm, morning sun and cooler, afternoon shade. Avoid planting in hot, dry, exposed sites. The best time to plant them is fall. Early spring is the next best planting time. With extra care, they can be planted at other times.

Blue or pink blooms depend on soil pH AND corresponding available aluminum. At lower pH levels (acid soils), aluminum is more readily available to the plant and flowers become blue. At higher pH ranges (more alkaline soils), aluminum is less available and flowers are pink. Want pink flowers? Add lime to raise soil pH. Want blue flowers? Add sulfur to lower soil pH.

Changing soil pH is a gradual process and requires a soil test for accuracy. Broadcast 1/2 cup of wettable sulfur per 10 square feet and water-in to make flowers blue. To make the flowers pink, broadcast one cup of dolomitic lime per 10 square feet and water it into the soil. Raising pH takes longer than lowering. It may be next year before a noticeable change to pink flowers.

A faster option for changing flower color is liquid soil drenches. Want to enhance your blue flowers or to change pink ones to blue? Dissolve one tablespoon of alum (aluminum sulfate) in a gallon of water and drench the soil around the plant in March, April and May. Desire pink flowers? Dissolve one tablespoon of hydrated lime in a gallon of water and drench the soil around the plant in March, April and May. Avoid splashing either of these solutions on leaves, bark, or skin as it can cause burning.

Afternoon shade is a must for hydrangeas. One inch of water per week is recommended, and of course, mulching helps conserve water loss and cool the root system.

If blue flowers are desired use fertilizers low in phosphorus (the middle number – 10-10-10). Phosphorus ties up aluminum making it unavailable for root uptake. This leads to pink flowers.
Periodic soil tests are recommended to ensure phosphorus levels remain at acceptable levels. Too much soil phosphorus causes plant injury.